In closures having a metal shell and depending skirt, it is very important that the shape of the synthetic resin liner installed inside the top of the shell have good sealing properties when applied to a container. In Japanese Patent Early Disclosure Number 53-65184, there is disclosed a liner having (a), an outer annular projection that provides an outer peripheral surface that is adapted to contact the outer peripheral surface of a mouth of a container to be sealed, and (b), an inner annular projection that provides an outer peripheral surface that contacts the inner peripheral surface of the mouth. Closures provided with liners of this type have sealing properties that are improved as compared to closures provided with liners of the types heretofore offered.
Experiments performed by the present inventors, however, have indicated that there is a problem in that the closures as described above have decreased sealing properties when they undergo impacts of considerable size.
It is therefore an object of the present invention to improve the shape of liners in closures of the type described above so that sufficient sealing properties will be retained even when these closures are subjected to considerable impact forces.